Fluid handling and storing of make-up refrigerant

ABSTRACT

Liquid cryogenic refrigerant is transferred from a pressurized transport vessel to a low-pressure supply tank in cryogenic refrigeration system by passing vapors from the vessel to the refrigeration system and passing the resulting cooled liquid from the vessel to the supply tank.

United States Patent Phillips Petroleum Company Appl. No. Filed Patented Assignee FLUID HANDLING AND STORING OF MAKE-UP REFRIGERANT [50] Field of Search 62/54, 55, 53, 292, 77, 510

[56] References Cited UNITED STATES PATENTS 2,850,882 9/1958 Starnes 62/55 X Primary ExaminerAlbert W. Davis, Jr.. Attorney-Young and Quigg 6 Claims 2 Drawing Figs ABSTRACT: Liquid cryogenic refrigerant is transferred from U.S. CII 62/53, a pressurized transport vessel to a low-pressure supply tank in 62/54, 62/55, 62/77, 62/292, 62/510 cryogenic refrigeration system by passing vapors from the ves- Int. Cl F170 7/02, sel to the refrigeration system and passing the resulting cooled F25b 45/00 liguid from the vessel to the supply tank. v m 7 Q REFRIGERATION SYSTEM J19 I42 U VAPOR RECOVERY FACILITIES 20 l8 5 TRANSPORT 1Q VESSEL UNLOADING ggi i S FACILITIES PUMPING AND EVAPORATION FACILITIES PATENTEDAUB31 |97| 3,602,002

SHEET 1 BF 2 REFRIGERATION SYSTEM vAPoR RECOVERY FAcII ITIES 2o SIa TRANSPORT Q VESSEL A l5 UNLOADING ZZ 3 FACILITIES I3 Iew 3 PUMPING AND EvAPoRATIoN FACILITIES INVENTORS D. M. BAILEY A T TORNE VS FLUID HANDLING AND STORING OF MAKE-UP REFRIGERANT Refrigerants such as methane, ethane, ethylene and the like are generally stored in large insulated storage tanks at low temperatures and at pressures approximating atmospheric pressure. In order to prevent the buildup of excessive pressure in the storage tank resulting from liquid vaporization, a vapor recovery system is provided to withdraw vapors from the tank, condense the vapors, and return the resulting liquid to the tank. These vapor recovery system facilities are designed to handle only the maximum boiloff rate of the refrigerant at extreme storage conditions. Consequently, when warm refrigerant at a high pressure from an external supply is introduced into the storage tank, the rate of vapor flow to the vapor recovery system rapidly increases to the full capacity of the system.

While the vapor recovery system effectively controls the storage tank pressure without loss of refrigerant, it limits the rate at which refrigerant from an external supply can be added to the storage tank to replace losses in the refrigeration system. Makeup refrigerant is usually delivered to the storage site in pressurized vessels such as trailer trucks or railroad car tanks. Heretofore a substantial period of time, frequently as long as 24 hours, has been required to transfer the refrigerant from the transport vessel to the storage tank because the vapors flashing from the relatively hot liquid entering the tank could not be handled any faster by the vapor recovery system.

In order to appreciate the present invention, it is necessary to understand the operation of a conventional refrigeration system, such as one employing ethylene as a refrigerant. Such a system often comprises a multistage refrigeration zone and a multistage compressor for circulating the refrigerant through the refrigeration zone. The design capacity of the compressor normally exceeds the anticipated rate of refrigerant circulated therethrough. In order to control the compressor operation within efficient limits, recycle facilities are provided to feed back some high-pressure refrigerant to the compressor suction line. The purpose of the recycle is to balance the load equally among the compressor stages and assure a minimum load on the compressor.

In accordance with this invention it has been found that by withdrawing vapors from the transport vessel and introducing these vapors into the suction of the refrigeration compressor, the pressure and hence the temperature of the liquid remaining in the transport vessel can be reduced to levels approaching those of the refrigerant in the storage tank. When the cooled refrigerant is then transferred from the transport vessel to the storage tank, the vaporization is relatively low. Consequently the capacity of the vapor recovery system is not unduly taxed so that a rapid transfer of the refrigerant to the storage tank can take place. It should be noted that under normal operation the refrigeration compressor, because of its designed overcapacity, can receive the vapors from the transport vessel at a rapid rate without seriously affecting the operation of the refrigeration system.

Briefly, the method of this invention comprises directing vapor flow from a transport vessel to the suction of a refrigeration compressor to reduce the pressure in the vessel, and directing liquid from the vessel into the storage tank. By employing this method, the unloading time for transport vessels v of some 7,000 gallons volume can be reduced to 2 or 3 hours or so.

In the drawing:

FIG. 1 is a schematic flow diagram illustrating the relation- I ship of the transport vessel, the storage tank, and the refrigeration system; and

FIG. 2 is a more detailed view of a specific embodiment of the system shown in FIG. 1.

As shown in FIG. 1, the refrigeration plant includes a storage tank 10, vapor recovery facilities 11, a refrigeration system 12, and pumping and evaporation facilities 13. Under normal operating conditions, boiloff vapor passes from the cryogenic storage tank 10 to the vapor recovery facilities 11 through flow path 14, and after being compressed and condensed is returned to storage tank 10 through flow path 115. When it becomes necessary to recharge refrigeration system 12, liquid refrigerant is passed through flow path 16 to pumping and evaporation facilities 13 and then to the refrigeration system 12 through flow path 17. When a transport vessel 13 arrives to replenish the ethylene in storage tank 10, the vapors are directed through flow path 19 to refrigeration system 12. This lowers the pressure and hence the temperature of the ethylene in transport vessel 18. Liquid ethylene is transferred to storage tank 10 through flow path 20.

As illustrated in detail in FIG. 2, a vapor removal conduit 21 and a liquid removal conduit 23 are connected to transport vessel 22 which in this illustration is a trailer truck. These conduits are supplied with respective cutoff valves 21a and 23a. As described in detail hereinafter, vapor conduit 21 leads to refrigeration system 12. The liquid from vessel 22 is transferred to storage tank 10 through conduit 23 which includes a pump 24 and a flow control valve 25. The flow through control valve 25 is regulated by the pressure in storage tank 10 by means of pressure controller 26. Flow through conduit 23 is limited to prevent excessive pressure buildup in tank 10. In order to regulate the pressure within tank 10 and refrigerate the ethylene contained therein, the vapor recovery and refrigeration unit 11 withdraws vapors from the tank, condenses and cools the vapors, and returns the resulting condensate. The vapor recovery and refrigeration unit 111 comprises a knockout drum 29 which receives vapors from the tank through conduit 27. The vapors pass from drum 29 through a conduit 31 to a compressor 30. The compressed vapors are then cooled in a cooler 32 and further cooled and condensed in a refrigeration condenser 33. The condensed liquid is returned to tank 10 through a conduit 34. The capacity of compressor 30 is generally sized to handle the maximum rate of vapor evolving through conduit 27 under anticipated extreme ambient storage conditions. For example, in a 7,000- barrel storage tank the maximum vaporization rate at storage conditions of -l 55 F. and a pressure of between 7-10 inches of water, is expected to be about 1470 lb./hr. Ethylene in the transport vessel 22 usually arrives at the loading facilities at a pressure of from about 30 p.s.i.g. to about 40 p.s.i.g. and a corresponding temperature of about 1 13 F. to about -l08 F. In a conventional unloading system, when the higher temperature ethylene begins entering storage tank 10 through line 23, vapors flash from the higher temperature ethylene and pass through conduit 27, thereby increasing the total vapor flow to the full capacity of the vapor recovery system 11. The resulting increased pressure in storage tank [[0 causes control valve 25 to throttle the flow through conduit 23 to a very low rate. In such a system, as long as 24 hours have been required to transfer the contents of a 7,000-gallon transport vessel to a storage tank.

The pumping and evaporation facilities 13 include a makeup conduit 36 provided with a pump 37, and an evaporator 38. Makeup ethylene from storage tank 10 is pumped through conduit 36 to evaporator 38 where the liquid ethylene is vaporized. The resulting vapors flow from evaporator 38 to the refrigeration system 12 through conduits 39 and 62. A conduit 73, having a valve 74 therein, extends from the outlet of cooler 32 to conduit 39 to permit cooled vapors to be passed directly to refrigeration system 12. Ethylene is delivered from tank 10 to evaporator 13 when required to replace lost refrigerant. This flow can be regulated by a temperature controller, not shown, in the refrigeration system.

The illustrated refrigeration system 12 comprises a multistage refrigeration zone 40 and two double-stage compressors 41 and 42. The multistage refrigeration zone 40 receives liquefied ethylene from a conduit 43. After expansion and vaporization in zone 40, relatively low-pressure gaseous ethylene passes therefrom through conduits 44 and 45 to the inlet of the first stage of a compressor 42. Similarly, intermediate pressure gaseous ethylene passes from the refrigeration zone 40 to the second stage of compressor 42 through conduits 46 and 47. Relatively high-pressure gaseous ethylene passes from refrigeration zone 40 to the second stage of a compressor 41 through conduits 48 and 49. The low-pressure gaseous ethylene received from suction line 45 joins with the intermediate-pressure ethylene received from conduit 47 for further compression in the second stage of compressor 42. The combined streams exit from compressor 42 through a conduit 50 and pass into the first stage of compressor 41 for a third stage compression. The compressed gaseous ethylene from the third stage joins with the high-pressure ethylene from a conduit 49 for fourth stage compression in compressor 41. The hot compressed gaseous ethylene leaves compressor 41 through a conduit 53, cooler 54 and enters a heat exchanger 56 wherein sufficient heat is withdrawn to liquefy the gaseous ethylene. From heat exchanger 56 the liquefied ethylene flows through a conduit 57 and conduit 43 to refrigeration zone 40. In order to balance the operation of the multistage compressor system, recycle conduits 58 and 59 interconnect the compressor discharge conduit 55 and the intermediate pressure conduit 47 and the suction conduit 45, respectively. Conduits 58 and 59 are provided with flow controllers 60 and 61, respectively, which can be responsive to the flows through conduits 47 and 45, respectively. The system is designed so that there is a constant flow to the compressor at all times. The flow through conduits 58 and 59 decreases as the flow through conduits 47 and 45 increases and vice versa.

At this juncture it should be observed that the refrigeration equipment thus far described represents a conventional plant. The present invention involves the addition of vapor removal conduit 21 which connects transport vessel 22 to the suction line 45 of the first stage compression zone of compressor 42. A conduit 61a extends from the junction of conduits 21 and 35 and joins with ethylene makeup conduit 39. A pressure controller 77 adjusts a valve 78 in conduit 61a. A conduit 62 interconnects this junction and suction line 45. Conduit 61a is provided with a shutoff valve 63. Pressure controller 77 regulates the pressure downstream of valve 63, whereby the rate of flow into suction line 45 can be controlled so as not to exceed the instantaneous capacity of compressor 42. Generally the suction pressure on compressor 42 will be in the order of l to 2 p.s.i.g. In order to reduce the pressure from 40 p.s.i.g. to 15 p.s.i.g. in a 7,000-gallon transport vessel containing ethylene, a total vapor flow of about 2,275 lbs is required. This flow to compressor 42 can be distributed over a period of approximately to 15 minutes. At this time the flow through recycle conduit 59 is reduced by an amount corresponding to the vapor flow from vessel 22. At the reduced pressure, e.g. l5 p.s.i.g., the temperature of the ethylene is approximately l3 1 F. Thus when ethylene is directed through liquid conduit 23 to tank 10, vapors flashing from the liquid will be substantially less than that experienced heretofore, permitting the tank to be unloaded in a fraction of the time previously required. In the example described, this unloading time can be reduced to about 2 to 4 hours. During the liquid unloading phase of the process when the pressure in truck 22 approaches the pressure in tank 10, vapor equalizer line 35 is opened to vapor conduit 21 by a pressure controller 80 which regulates a valve 81. During the normal unloading time, some vapor may pass from truck 22 through conduit 35 to drum 29. If desired, the pressure in vessel 22 can be reduced even further to a range of 5-l5 p.s.i.g. before ethylene is directed through liquid conduit 23 to tank 10.

In summary, the process according to this invention comprises reducing the pressure in transport vessel 22 to a level slightlyabove the pressure in storage tank by directing vapor flow to the suction of compressor 42; and then directing liquid flow from the vessel 22 to tank 10 by starting pump 24. Reduction of pressure in vessel 22 cools the liquid ethylene therein so that when the liquid enters the tank, excessive flash vaporization does not occur. Thus the vapor recovery and refrigeration system can adequately handle the small amount of vapors four from the entering ethylene and evolving from the stored ethylene. Consequently, control valve 25 is throttled very little. A vent conduit 28a having a control valve 28 therein'is connected to conduit 35. If an excessive pressure should be reached in tank 10, controller 26 sends out a signal to open valve 28.

The unloading time for a transport vessel 22 of course will depend upon the volume capacity and the storage conditions of the ethylene contained therein. However, for an 8,000-gallon vessel having a storage pressure of 40 p.s.i.g. and temperature of -l08 F the total unloading time will be about 2-4 hours. The loading time for the same vessel using the prior art method usually required about 24 hours. It should be observed that the unloading method according to this invention achieves four objects: (1) transfer of the refrigerant from the transport vessel to the storage tank in a relatively short period of time; (2) transfer of the refrigerant from the transport vessel to the storage tank without loss of refrigerant,'(3) recharging of the refrigeration system, and (4) reduction of the size of the vapor recovery and refrigeration facilities.

While this invention has been described in conjunction with a presently preferred embodiment, it should be evident that it is not limited thereto.

What is claimed is:

l. The method of transferring liquid cryogenic refrigerant from a pressurized supply'vessel to a low pressure refrigerant source for a cryogenic refrigeration system, which system includes a refrigerant expansion zone and a refrigerant compression zone, comprising the steps of:

reducing the pressure in the supply vessel to cause cooling of the liquid refrigerant therein by passing refrigerant vapor from the supply vessel to the suction of the compression zone; and

passing the resulting cooled liquid refrigerant from the supply vessel to the refrigerant source.

2. The method of claim 1, further comprising the step of controlling the temperature and pressure of the refrigerant source by withdrawing boiloff vapors from said source and passing the withdrawn vapors through a refrigeration unit to compress and condense the vapors, and returning the resulting liquid to said source.

3. The method of claim 1 wherein the step of controlling pressure includes controlling the flow of liquid from the supply vessel as a function of the pressure of the refrigerant source to prevent excessive pressure from building up in said source.

4. The method of claim 1 wherein said ethylene.

5. In a refrigeration system that includes a primary refrigeration unit having a compressor and an expansion means; a refrigerant storage tank; and a secondary refrigerant unit connected to said tank to compress boiloff vapors, cool the compressed vapors, and return the resulting condensate to the storage tank; improved apparatus in combination with a transport vessel for delivering refrigerant from said transport vessel to the system, comprising: first conduit means connected at one end to the inlet of said compressor, the second end of said first conduit means being connected to an upper region of the transport vessel to withdraw refrigerant vapors; second conduit means connected at one end to said storage tank, the second end of said second conduit means being connected to a lower region of the transport vessel to withdraw liquid refrigerant; and a pump in said second conduit means.

6. The apparatus of claim 5, further comprising a valve in said second conduit means, means to measure pressure in said tank, and means responsive to said means to measure pressure to control said valve.

refrigerant is 

1. The method of transferring liquid cryogenic refrigerant from a pressurized supply vessel to a low pressure refrigerant source for a cryogenic refrigeration system, which system includes a refrigerant expansion zone and a refrigerant compression zone, comprising the steps of: reducing the pressure in the supply vessel to cause cooling of the liquid refrigerant therein by passing refrigerant vapor from the supply vessel to the suction of the compression zone; and passing the resulting cooled liquid refrigerant from the supply vessel to the refrigerant source.
 2. The method of claim 1, further comprising the step of controlling the temperature and pressure of the refrigerant source by withdrawing boiloff vapors from said source and passing the withdrawn vapors through a refrigeration unit to compress and condense the vapors, and returning the resulting liquid to said sourCe.
 3. The method of claim 1 wherein the step of controlling pressure includes controlling the flow of liquid from the supply vessel as a function of the pressure of the refrigerant source to prevent excessive pressure from building up in said source.
 4. The method of claim 1 wherein said refrigerant is ethylene.
 5. In a refrigeration system that includes a primary refrigeration unit having a compressor and an expansion means; a refrigerant storage tank; and a secondary refrigerant unit connected to said tank to compress boiloff vapors, cool the compressed vapors, and return the resulting condensate to the storage tank; improved apparatus in combination with a transport vessel for delivering refrigerant from said transport vessel to the system, comprising: first conduit means connected at one end to the inlet of said compressor, the second end of said first conduit means being connected to an upper region of the transport vessel to withdraw refrigerant vapors; second conduit means connected at one end to said storage tank, the second end of said second conduit means being connected to a lower region of the transport vessel to withdraw liquid refrigerant; and a pump in said second conduit means.
 6. The apparatus of claim 5, further comprising a valve in said second conduit means, means to measure pressure in said tank, and means responsive to said means to measure pressure to control said valve. 